maar

Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

n. A flatbottom, roughly circular volcanic crater of explosive origin that is often filled with water.

from Wiktionary, Creative Commons Attribution/Share-Alike License

n. a broad volcanic crater, usually filled with a lake

from The Century Dictionary and Cyclopedia

n. In geology:

n. A local German name originally applied to certain small crater-lakes in the recently extinct volcanic region of the Eifel, near Bonn, on the Rhine. The craters were believed to have resulted from explosive outbreaks, without emissions of lava.

n. Technically, any crater which has been produced by an explosion unaccompanied by lava.